1. Field of the Invention
The present invention relates to vibration gyroscopes, and more particularly, to a vibration gyroscope for detecting a rotation angular velocity with the use of bending and vibration of a vibration member.
2. Description of the Related Art
FIG. 10 is a diagram showing an example of a conventional vibration gyroscope. This vibration gyroscope 1 includes a vibrator 2. The vibrator 2 includes a vibration member 3 having, for example, a regular triangular prism shape, as shown in FIG. 10. On the three side faces of the vibration member 3, three piezoelectric elements 4a, 4b, and 4c are formed, respectively. The piezoelectric elements 4a and 4b are used for driving the vibrator 2 to bend and vibrate, and also for detection in order to obtain the signal corresponding to a rotation angular velocity. The piezoelectric element 4c is used in a feedback loop for driving the vibrator 2.
Between the piezoelectric elements 4a and 4b, and the piezoelectric element 4c, an oscillation circuit 5 is connected through resistors. The vibration member 3 is used as a grounding terminal and is connected to a point having half the power voltage. The signals output from the piezoelectric elements 4a and 4b are input to a differential circuit 6. The signal output from the differential circuit 6 is detected by a synchronous detection circuit 7 in synchronization with the signal of the oscillation circuit 5. The signal output from the synchronous detection circuit 7 is smoothed by a smoothing circuit 8 and amplified by a DC amplifier 9.
When the driving signal shown in FIG. 11 is applied to the two piezoelectric elements 4a and 4b in the vibration gyroscope 1, the vibration member 3 bends and vibrates in the direction perpendicular to the surface where the piezoelectric element 4c is formed. When the vibration member 3 rotates about its axis, the direction of vibration of the vibration member 3 changes due to the Coriolis force. Therefore, the signals output from the piezoelectric elements 4a and 4b are different. The signal corresponding to a rotation angular velocity can be obtained by calculating the difference between the signals output from the piezoelectric elements 4a and 4b. The signal output from the differential circuit 6 is detected by the synchronous detection circuit 7, smoothed by the smoothing circuit 8, and amplified by the DC amplifier 9. By measuring this signal, the rotation angular velocity applied to the vibrator 2 can be detected.
Since in such a vibration gyroscope the grounding terminal is connected to a point having half the power voltage, voltage A, which is only half the maximum power voltage, is applied to the piezoelectric elements used for driving, as shown in FIG. 11. Therefore, when a low-voltage power supply such as a dry cell is used, sufficient excitation cannot be applied to the vibration member. If the vibration member is not sufficiently excited, the sensitivity of the vibration gyroscope decreases. As a countermeasure to this problem, a peripheral circuit has conventionally compensated for a decrease in the sensitivity. When this countermeasure is used, vibrator noise and circuit noise are also amplified, and the S/N ratio is reduced.